The present invention relates to thermoplastic molding compositions. In particular, the invention relates to colored thermoplastic compositions and articles molded therefrom.
Lighting reflectors, especially for automotive applications, require materials that can withstand the high heat produced by light sources, that have excellent dimensional stability to focus the light in a tight pattern at long distances, and that can be easily processed into complex shapes. These reflectors are usually coated with a metal, such as aluminum, to provide a highly reflective surface. To achieve this high degree of reflectivity with low haze, a very smooth pre-coated surface is required. In order to consistently achieve such a smooth pre-coated surface, it has typically been necessary to base coat the molded reflector with a primer prior to coating the reflector with metal. Efforts to simplify production of these metalized plastic articles by coating metal directly onto the molded reflector have resulted in intolerable waste because of difficulty identifying defective molded articles before the metal coating has been applied. The defective articles have surface blemishes that become noticeable only after a metal coating is applied, causing the parts to be discarded and creating an inefficient use of the coating equipment as well as loss of the thermoplastic resin. Direct metalization of molded parts is also challenging because it introduces the additional requirements of good adhesion of the metal to the molded part and a very smooth surface of the part as molded.
There is therefore a need for molded reflectors satisfying the simultaneous requirements of high temperature stability, high surface smoothness, good adhesion to metal coatings, and ready detectability of surface defects in the reflectors as molded, as well as high reflectivity, low haze, and low diffuse reflectivity after metalization.
High temperature stability, high surface smoothness, good adhesion to metal coatings, and ready detectability of surface defects are provided by an article comprising: (a) a single phase amorphous thermoplastic resin or resin blend having a glass transition temperature (Tg) not less than about 170xc2x0 C.; and (b) at least one colorant; wherein a surface of the article exhibits a CIE lightness value (L*) not greater than about 50, and a 20xc2x0 gloss value per ASTM D523 not less than about 100.
Molded articles suitable for direct metalization comprise: (a) a single phase amorphous thermoplastic resin or resin blend having a glass transition temperature (Tg) not less than about 170xc2x0 C.; and (b) at least one colorant; wherein a surface of the article exhibits a CIE lightness value (L*) not greater than about 50, and a 20xc2x0 gloss value per ASTM D523 not less than about 100. After metalization, a surface of the article exhibits a haze value not greater than about 1%, and a diffuse reflectivity not greater than about 1%.
We have discovered that to obtain a directly metalized article with high dimensional stability, a high degree of reflectivity, low diffuse reflectivity, and low haze, it is important that the article comprise a single phase amorphous polymeric resin or resin blend and be substantially free of solid particles and particle aggregates that can detract from the above properties. The use of single phase amorphous resins, rather than crystalline resins, improves the dimensional stability of the molded articles. Limiting the amounts of solid particles and particle aggregates is preferred to ensure high gloss in the article as molded, and low haze and low diffuse reflectivity after the article is metalized. While an unfilled, uncolored resin, like polyetherimide resin, can be directly metalized to give a low haze, high gloss surface that can withstand high heat, it is often difficult to detect blemishes on such transparent articles and discard blemished articles prior to metalization and coating operations. We have found that articles molded from dark thermoplastic resin compositions make surface blemishes, such as splay and shark skin, more noticeable in visual inspections. Thus, the use of dark compositions facilitates visual identification of blemishes prior to metalization, thereby reducing waste and expense. In addition, a partially metalized article may have transparent portions that allow some light to escape. This escaped light may interfere with focusing the light from such a lamp; for instance an unmetalized ring of transparent resin surrounding the bulb opening can create an undesired halo around the bulb. The dark compositions of the invention prevent this problem. We have also found that known opacifying techniques, such as the addition of standard colorants, like titanium dioxide or carbon black, and the addition of non-miscible polymers (such as polyolefins or polycarbonates), cause unacceptable losses of surface smoothness and gloss, and increased haze and diffuse reflectivity of the articles once metalized.
Single phase amorphous thermoplastic resins suitable for use in the articles include polyetherimides, polyarylethers, polyethersulfones, polysulfones, polycarbonates, polyestercarbonates, polyarylates, polyamides, polyesters, and single phase blends comprising at least one of the foregoing resins. The use of polyetherimides and single phase blends comprising polyetherimides, such as polyester polyetherimide blends, is presently preferred. The thermoplastic resin or resin blend has a glass transition temperature, Tg, greater than about 170xc2x0 C., preferably greater than about 185xc2x0 C., more preferably greater than about 200xc2x0 C. The thermoplastic resins above are generally commercially available, and methods for their synthesis and blending are well known in the art.
While the proportion of thermoplastic resin or resin blend in the article may vary considerably, it is generally at least 80% by weight of the article. In a preferred embodiment, the thermoplastic resin or resin blend is present at about 90 to 99.99 weight percent, preferably about 95 to 99.99 weight percent, more preferably about 97 to 99.99 weight percent.
Synthetic colorants are typically derived from coal tar or petroleum intermediates. Colorants of many distinct types are available for use in plastics and coatings. The Color Index names many different chemical classes of colorants, including, for example, nitroso, nitro, mono azo, diazo, triazo, polyazo, azoic, stilbene, carotenoid, diphenylmethane, triarylmethane, xanthene, quinoline, acridine, methine, thiazole, indamine, indophenol, azine, oxazine, thiazine, sulfur, lactone, aminoketone, hydroxyketone, anthraquinone, indigloid, and phthalocyanine, as well as inorganic pigments. Colorants may be organic or inorganic, dyes or pigments.
Dyes are colorants that do not normally scatter light but absorb light at some visible wavelength. Dyes are often soluble, at some concentration, in the polymer matrix of a colored article. Pigments are organic or inorganic colorants that are usually present in a matrix as discrete particles insoluble in the matrix. The designation of a given colorant as pigment or dye will depend on the polymer matrix, colorant concentration and crystallinity, temperature, and other factors. Preferred colorants are soluble in the matrix resins at the concentrations employed to color the article.
Colorants suitable for use in the articles also generally exhibit high extinction coefficients and high thermal stability. High thermal stability is defined as the absence of significant color shift or thermal degradation when processed at temperatures of 250-350xc2x0 C. required to form the articles of the invention from the resins indicated above. In addition, the colorants should not attack or degrade the resin resulting in an unacceptable loss of mechanical properties or generation of gaseous by-products during molding.
Suitable colorants having good thermal stability include those known under their Color Index numbers as solvent green 3, solvent green 28, solvent red 52, solvent red 111, solvent red 135, solvent red 169, solvent red 179, solvent red 207, disperse red 22, vat red 41, solvent orange 60, solvent orange 63, solvent violet 13, solvent violet 14, solvent violet 50, amino ketone black, solvent black 7, nigrosine dyes, disperse blue 73, solvent blue 97, solvent blue 101, solvent blue 104, solvent blue 138, disperse yellow 160, solvent yellow 84, solvent yellow 93, solvent yellow 98, solvent yellow 163, solvent yellow 160:1, and mixtures comprising at least one of the foregoing colorants. Preferred colorants include solvent red 135, solvent red 179, amino ketone black, solvent black 7, solvent violet 13, solvent violet 14, solvent violet 36, solvent violet 50, disperse blue 73, solvent yellow 93, solvent green 3, disperse yellow 160, and mixtures comprising at least one of the foregoing colorants.
Colorants are employed in amounts and combinations sufficient to render the molded article dark and opaque, and more specifically to provide the lightness values described below. The specific amount of a colorant employed will depend on, among other factors, its solubility and extinction coefficient in the thermoplastic matrix, and whether it is being employed in combination with one or more additional colorants. Suitable amounts and combinations are readily determined by those of ordinary skill in the art. Typical colorant amounts are about 1xc3x9710xe2x88x924 to about 5 parts per hundred parts resin by weight. Preferred colorant amounts are about 1xc3x9710xe2x88x924 to about 0.5 parts per hundred parts resin by weight.
The article may, optionally, also contain various additives known in the art, including phosphite antioxidants, such as, for example, tris(nonyl-phenyl) phosphite and tris(2,4-di-t-butylphenyl)phosphite; hindered phenol antioxidants, such as, for example, alkylated polyphenols, including, for example, tetra-cis(methylene)-3,5-di-t-butyl-4-hydroxycinnamate; and other additives such as, for example, UV absorbers, light stabilizers, lubricants, plasticizers, and anti-static agents.
It is preferred that the molded article be substantially free of particles that, individually or in aggregate form, would be detrimental to achieving the as molded values of 20xc2x0 gloss, and the post-metalized values of reflectivity, haze and diffuse reflectivity, as detailed below. While authoritative determination of tolerable amounts and particle sizes of particulate components relies on the tests for gloss, reflectivity, haze, and diffuse reflectivity described herein, it has been observed that particulate components present at as little as 0.3 parts per hundred parts resin by weight and having particle sizes greater than about 13 nanometers may contribute to surface defects. It is therefore preferred that the article be substantially free of particles having any dimension greater than about 10 nanometers, preferably substantially free of particles having any dimension greater than about 5 nanometers. By substantially free, it is meant that particles having sizes exceeding the above limits should comprise no more than about 0.2 weight percent of the total article. It is preferred that particles having sizes exceeding the above limits should comprise no more than about 0.1 weight percent of the total article, and more preferred that particles having sizes exceeding the above limits should comprise no more than about 0.05 weight percent of the total article.
The level and type of particles, and aggregates of particles, which may be acceptable in the articles of the invention must be such that the as molded article and any metalized articles derived directly from it will have the 20xc2x0 gloss, high reflectivity and low diffuse reflectivity described herein. The molded article possesses a surface having a CIE lightness value, L*, not greater than about 50, preferably not greater than about 40, more preferably not greater than about 35, yet more preferably not greater than about 31, and even more preferably not greater than about 30. The method of measuring L* values is described in R. McDonald, ed., xe2x80x9cColour Physics for Industry, 2nd Editionxe2x80x9d, The Society of Dyers and Colourists, Bradford, UK (1997). Low lightness values, as specified above, correspond to a dark (e.g., black, gray or blue) appearance that facilitates visual inspection of molded parts for defects.
The molded article possesses a surface exhibiting a 20xc2x0 gloss value per ASTM D523 of not less than about 100, preferably not less than about 110, more preferably not less than about 130. Such a high gloss surface in as molded articles is associated with high reflectivity, low diffuse reflectivity, and low haze after metalization.
The molded article may further comprise a metallic coating. The metal employed in the coating may include aluminum, silver, gold, nickel, palladium, platinum, copper, and alloys comprising at least one of the foregoing elements. Metal coatings comprising aluminum are presently preferred. Any known method for forming or adhering a metal coating on a thermoplastic substrate may be employed. Such methods include sputtering, vacuum metal deposition, vapor arc deposition, plasma chemical vapor deposition, thermal vapor metal deposition, and ion plating. Sputtering is a presently preferred method for forming or adhering a metal coating on the molded article.
Although the molded articles are well suited for direct application of a metal coating, it is also possible to pre-coat the molded article with a primer before applying the metal coating. It is also advantageous to further coat the metalized article with a clear layer to protect the metal surface from scratching, oxidation, or related problems. Silicone-derived clear coats, often deposited by plasma based silicone polymerization, are presently preferred.
The metalized surface of the article has a total reflectivity not less than about 85%, preferably not less than about 90%, more preferably not less than about 91%. The metalized surface also has a diffuse reflectivity not greater than about 1%. The metallized surface further has a haze value not greater than about 1%.
The compositions discussed herein can be prepared by a variety of melt blending techniques. Use of a vacuum vented single or twin screw extruder with a good mixing screw is preferred. In general, the melt processing temperature at which such an extruder should be run is about 100 to about 150xc2x0 C. higher than the Tg of the thermoplastic. The mixture of ingredients may all be fed together at the throat of the extruder using individual feeders or as a mixtures. In some cases, for instance in blends of two or more resins, it may be advantageous first extrude a portion of the ingredients in a first extrusion and then add the remainder of the mixture in a second extrusion. It may be useful to first precompound the colorants into a concentrate which is subsequently mixed with the remainder of the resin composition. In other situations it may be beneficial to add portions of the mixture further down stream from the extruder throat. After extrusion the polymer melt is preferably stranded and cooled prior to chopping or dicing into pellets. Preferred pellets are about {fraction (1/16)} to xe2x85x9 inch long. The pelletized thermoplastic resins are then dried to remove water and molded into the articles of the invention. Drying at about 135 to about 150xc2x0 C. for about 4 to about 8 hours is preferred, but drying times will vary with resin type. Injection molding is preferred using suitable temperature, pressures, and clamping to produce articles with a glossy surface. Melt temperatures for molding will be about 100xc2x0 to about 200xc2x0 C. above the resin Tg. Oil heated molds are preferred for higher Tg resins, Mold temperatures can range from about 50 to about 175xc2x0 C. with temperatures of about 120xc2x0 to about 175xc2x0 C. preferred. Many variations of these compounding and molding conditions can be employed by those skilled in the art to make the compositions and articles of the invention.
The invention encompasses a method of preparing a reflective article, comprising: molding an article comprising (a) a single phase amorphous thermoplastic resin or resin blend having a glass transition temperature (Tg) not less than 170xc2x0 C., and (b) at least one colorant, to form a molded article having a surface exhibiting a CIE lightness value (L*) not greater than 50, and a 20xc2x0 gloss value per ASTM D523 not less than 90; and coating the surface of the molded article with a reflective metal to form a metalized surface having a haze value not greater than about 1% and a diffuse reflectivity not greater than about 1%.
The invention also encompasses a molded thermoplastic composition, comprising: (a) about 90 to 99.99 weight percent of a single phase amorphous thermoplastic resin or resin blend selected from the group consisting of polyetherimides, polyarylethers, polyethersulfones, polysulfones, polycarbonates, polyestercarbonates, polyarylates, polyamides, polyesters, and single phase blends comprising at least one of the foregoing resins, wherein the single phase amorphous thermoplastic resin or resin blend glass transition temperature Tg not less than about 170xc2x0 C.; and (b) about 1xc3x9710xe2x88x924 to about 5 weight percent of a colorant selected from the group consisting of solvent green 3, solvent green 28, solvent red 52, solvent red 111, solvent red 135, solvent red 169, solvent red 179, solvent red 207, disperse red 22, vat red 41, solvent orange 60, solvent orange 63, solvent violet 13, solvent violet 14, solvent violet 50, amino ketone black, solvent black 7, disperse blue 73, solvent blue 97, solvent blue 101, solvent blue 104, solvent blue 138, disperse yellow 160, solvent yellow 84, solvent yellow 93, solvent yellow 98, solvent yellow 163, solvent yellow 160:1, and mixtures comprising at least one of the foregoing colorants.